Settable neutron radiation shielding material



Nov. 22, 1960 l. R. AXELRAD 2,961,415

SETTABLE NEUTRON RADIATION SHIELDING MATERIAL Filed Nov. 2, 1956 Neutron Shield i Radioactive Area l2 l0 5 I Gamma Ray shield Fig.1.

WITNESSES INVENTOR lrving R.AxeIrc|d SETTABLE NEUTRON RADIATION Santana Marrnmr.

Filed new 195d,; Ser. N 620,141 4 class; (Ci. 252-478 The, present invention relates to neutron radiation shieldingmaterial and has particular reference to settable compositions adapted for application about radioactive areas to. attenuate fast moving neutrons and capture slowmoving neutrons. v 1

.In the building of apparatus utilizing radioactive materials,the,shielding of the radioactive area against the escape =therefrom of harmful radiation products is of prime importance. In general, almost all radioactive areas are, provided with. a primary shielding coating of lead, tungsten, or other, dense material which is, effective in preventing the passage therethrough of gamma rays. Neutrons, however, are capable of passing through lead or tungsten shields. for land based radioactive equipment, water and concrete frequently are used as shields to prevent the escape of neutrons therefrom. Neither water nor concrete is completely suitable for use, however, for shielding radioactive equipment based on marine vessels. Water introduces corrosion problems, the solution of which require the use of relativelyexpensive corrosion inhibitors and the like. Accidental-puncture of containers intended for maintaining the water shieldin its proper location may result in a partialhorcomplete loss of the shield. The use of concreteas a neutron shield on marine based radioactive equipment is not ,desirable since thick sections are required foritnto function effectively. Such sections are extremely heavy and bulky and are not desirable for use on marine vessels.

It has been determined that certain chemical compositions constitute highly effective neutron shields which may be advantageously used in place of water or concrete. Thus, certain high hydrogen content chemical compositions are capable of attenuating fast moving, neutrons. Moreover, it hasbeen determined that boron and compounds thereof are capable of capturing slow moving thermal neutrons.

Polyethylene is one relatively high hydrogen content material. which has been used to provide a neutron shield about radioactive areas. Also, in some instances boron, or compounds thereof, has-been incorporated in the polyethylene. Heretofore, polyethylene, with or without boron therein, has been used only in sheet or slab form. Such sheets or slabs are not completely suitable for use when it is necessary to shield reactor parts having spherical surfaces, S-bends and other irregular shapes.

'The object of the present invention is to provide a settable, viscous, putty-like composition adapted for application as by troweling, casting, or the like about irregularly shaped members to provide a shield capable of attenuating fast moving neutrons and capturing slow moving neutrons.

Another object of the present invention is to provide a solid resinous composition adapted for mounting about members enclosing a radioactive area, which composition 'will'attenuate-fast moving neutrons and capture slow moving-neutrons; p

* Still another object of the'present invention is to provide a settable, viscous, putty-like resinous composition moving neutrons Zflfiififi I Patented Nov. 22, 1960 2 which comprises a material having a high ratio of hydrogen atoms to all other atoms in the resin in intimate combination with boron or a compound thereof in a suitable carrier.

Yet another object of this invention is to provide a viscous, putty-like resinous composition which is settable to a solid and which comprises a resinous carrier intimately associated with boron or a compound thereof and a material having a high ratio of hydrogen atoms to all other atoms in the material.

Still another object of the present invention is to provide a process for applying a pasty, putty-like composition to a member enclosing a radioactive area, said composition comprising a resinous carrier which is settable to a solid and which is intimately associated with boron or a compound thereof and a material having a high ratio of hydro gen atoms to all other atoms in the material.

Other and further objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a more complete understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawing, in which:

Figure 1 is. a diagrammatic cross-sectional view of a radioactive area shielded with the composition of this invention; and

Fig. 2 is a view, partially, in cross-section, of an irregularly shaped structural component, adapted for carrying radioactive material, having a shielding layer composed ofthe composition of this invention.

In the attainment of the foregoing objects and in accordance ,witlr; the present invention, there are provided settablemesinous compositions adapted to attenuate fast and capture slow moving neutrons comprising (1) a carrier which is curable to a solid and which is intimately associated with (2) a major proportion of a compound having ahigh ratio of hydrogen atoms to all other atoms in the material in combination with (3) a minor proportion of boronor compounds thereof.

The carrier portion of the compositions of this invention is. a fluid resinous material in which the other components of the composition are dissolved, dispersed, suspended, or otherwise distributed. Resinous materials which are suitable for use as carriers in this invention incude liquid or. relatively high viscosity pasty-like castable resins. which cure or set to solids, generally in the presence of a catalyst, hardener, or cure accelerator, eitherat room temperature or at somewhat higher temperatures. Examples of resinous materials which are suitable carriers include fluid polyesters, epoxy resins, castable phenol-aldehyde resins, butadiene polymers and copolymers thereof with styrene, and butadieneacrylonitrile copolymers. j

Other resinous materials which are suitable for use as carriers in accordance with this invention comprise materials known as plastisols. These are dispersions of a resin (or a material which forms a resin when admixed with a plasticizer) in a plasticizer. Examples of such resins include chloroprene polymers and copolymers; vinyl halide and vinylidene halide resins suchas polyvinyl chloride, polyvinylidene bromide, polyfiuorochloroethylene; vinyl chloride and vinylidene chloride copolymers; copolyrners of vinyl halides and vinylidene halides with other unsaturates such'as vinyl chloride with vinyl acetate, vinylidene bromide with vinyl acetate, and ethylene with vinyl chloroa'c'etate; halogenated high molecular weight natural resinsand hydrocarbons such as the commercially available halogenated paraffin waxes, the halogenated natural rubbers, and the like.

Examples of plasticizers which are suitable for main preparing plastisols in accordance with this invention include di-iso-octyl phthalate, discapryl phthalate, di-noctyl phthalate, butyl benzyl phthalate, di-Z-ethylhexyl phthalate, dibutyl phthalate, dioctyl azelate, dioctyl adipate, dioctyl sebacate, dibenzyl sebacate, tricresyl phosphate, tri-iso-octyl phosphate, octyl diphenyl phosphate, tri-Z-ethylhexyl phosphate, propylene glycol diacetyl ricinoleate, methyl acetyl ricinoleate, tetrahydrofurfuryl oleate and tetraethylene glycol di-isohexoate. The plasticizers may be used singly or in any suitable admixture of two or more.

In general, the plastisols must be heated to temperatures in excess of 100 C. to effect a satisfactory cure thereof. Therefore, the plastisols are particularly suitable for use as carriers in the compositions of this invention when it is desired to precast irregularly-shaped shielding sections in the shop and later mount such sections in place about the radioactive area. Other resins, such as the castable phenol-aldehyde resins, epoxy resins, and the like, which are curable at room temperature are particularly suitable for use as carriers in the compositions of this invention when it is desired to apply the compositions directly about an irregularly-shaped part, as by troweling, and permit it to harden, set, or cure in place.

Boron is incorporated in the compositions of this invention in amounts within the range of about 0.3% to 10% by weight of the total composition and may be employed either as the pure element or in any of its compounds. Thus, finely divided amorphous boron, boric acid, boric oxide, and boron carbide have been successfully used in accordance with this invention. Borax also is satisfactory for use in certain circumstances, although care is required to prevent water evolving therefrom when it is incorporated in resinous carriers which require heating to cure them to a solid state. Esters of boron such as glyceryl borate also may be used in the resinous composition.

The compound having the high hydrogen atom content which forms an essential component of the composition of this invention may comprise any one or more of those compounds which have a ratio of hydrogen atoms to all other atoms therein within the range of 0.5 :1 to 2:1. The material should be one which will not inhibit the satisfactory cure of the resinous carrier. Moreover, to be completely satisfactory, it must be a material which itself is not adversely affected by the conditions necessary to cure the resinous carrier. The high hydrogen content component of the present compositions may be a solid, a liquid, or have a viscosity anywhere between the extremes of liquids and solids, and it may be soluble in the resinous carrier, prior to the final cure or setting of the carrier, or dispersable, suspendable, or otherwise distributable in the carrier. Examples of materials having a hydrogen atom content within the range specified above which are suitable for use in accordance with this invention include polyethylene, butyl rubber, paraffin, polyisobutylene, and polyisoprene. These materials may be used alone or in mixtures of tWo or more in granular, pellet, fiake, powdered, or other particulate form. They may be employed in the compositions of this invention in amounts within the range of from about 10% to 85%, and preferably about 25% to about 75% by weight based on the total weight of the composition.

To formulate the compositions of this invention it is only necessary to admix the three essential components, viz., (1) the carrier, (2) the high hydrogen content material, and (3) boron, or a compound thereof. These components, if desired, may be admixed conveniently in a manner similar to the mixing of concrete using a hoe and mortar box. The resinous carrier together with a catalyst, hardener, or cure accelerator therefore is analogous to the water and cement portion of concrete; the high hydrogen content material, in particulate form, and boron or a compound thereof are analogous to the sand-gravel or solid portion of concrete. The compositions, when thoroughly admixed, have a viscous, putty- 4 like consistency and they either may be poured into suitable forms or applied about surfaces to be shielded by troweling or the like and permitted to harden or set to a solid in place.

In order to indicate even more fully the nature and capabilities of the present invention, the following specific examples are set forth. The parts given are by weight unless otherwise indicated.

Example I A fluid-pasty composition was prepared by thoroughly admixing (1) 64 parts of an epoxide resin (Bakelite RR18774), 24 parts of triethylenetetramine, (2) 30 parts of polyethylene (60 mesh), 61 parts of polyethylene /s" granules), and (3) 5 parts of boron carbide. The composition had a polyethylene content of approximately 50.8% by weight. It was introduced into a sheet metal housing member disposed about a pipe adapted for carrying radioactive material. The composition was tamped into the space surrounding said pipe to fill completely all the space therein. The material was found to be suitable in preventing the passage of both fast moving and slow moving neutrons from the radioactive area within the pipe to the surrounding atmosphere. To test the shock resistance of this material, a quantity thereof was cast into a block 12 inches x 12 inches x 8 inches and then subjected to 20 impacts of 2000 ft. lbs. No cracking or chipping occurred. Furthermore, the adhesion to the walls of the container in which the test block specimen was cast was excellent since no loosening of the block from the container walls was observed. The impact which the specimen survived is believed to be greater than that which it would receive in actual service on a marine vessel.

Example II A high hydrogen content composition was prepared by thoroughly admixing 1) 7 lbs. 8 ozs. of a phenolformaldehyde resin (Marblett #71), 11 ozs. of dilute hydrochloric acid, (2) 2 lbs. 6 ozs. of polyethylene (60 mesh) 5 lbs. 7 ozs. of polyethylene cubes), and (3) 1 lb. of boric acid. When troweled about irregular sections of an atomic reactor and cured, this composition was effective in preventing the escape of neutrons from the radioactive area to the outside.

A portion of this material was cast into a cake measuring 3 inches x 12 inches x 12 inches and tested for flammability. The test specimen was placed on edge and the flame from an oxygen-natural gas torch (about 5700 F.) was directed on the surface of the block near its center. The tip of the torch was maintained at a distance of approximately one inch from the surface of the block for a period of about two minutes and then removed. The flame produced by the torch extinguished itself in 38 seconds and exhibited no tendency toward spreading. The boric acid in this formulation provided boron atoms useful in the absorption of slow moving thermal neutrons and also increased the resistance of the cast sample to burning.

The following are examples of formulations which, when thoroughly admixed, provide viscous, putty-like compositions adapted for casting neutron shields of predetermined shape and compositions adapted for application directly by troweling or the like about structural components in radioactive areas to prevent the escape therefrom of neutrons.

Example III Parts Polyester resin 11 Benzoyl peroxide (catalyst) l Paraffin Boric oxide 3 Plastisol (dispersion of polyvinyl chloride in di-isooctyl phthalate) 24 Paraffin Polyethylene A: inch granules) 7O Boron carbide 1 Looking at the accompanying drawing, Fig. l is a view illustrating in schematic form the use of the composition of this invention. As shown on the drawing, a radioactive area or source 10 is completely surrounded by a metal housing 12 which may be of metal such as steel, stainless steel, aluminum or the like. Surrounding the housing 12 there is a primary shielding layer 14. This shield serves to prevent the passage of gamma rays from the radioactive area to the outside. Shield 14 may be constructed of any dense material such as lead, tungsten, or the like. Completely surrounding shield 14 is a secondary shield 16 composed of the composition of this invention. Shield 16 comprises a solid resinous carrier containing a compound having a high hydrogen atom content such as polyethylene, and boron or a compound thereof.

Fig. 2 partly in cross-section, illustrates the applicability of the settable compositions of this invention to irregularly-shaped structural components adapted for carrying radioactive material. A stainless steel pipe 18, through which may flow radioactive material, has a bend 20 which cannot be shielded conveniently by the application thereto of slab-s or sheets of shielding material. An eflective neutron radiation shield is provided in accordance with this invention by applying, as by troweling, a quantity of the shielding composition 22 of this invention about the bend 20 in pipe 18. Composition 22 is composed of particles of a compound 24 having a high hydrogen atom content such as polyethylene, boron carbide particles 26, and a cured resinous filler 28.

While the present invention has been described with respect to a preferred embodiment thereof, it will be understood, of course, that certain changes, modifications, substitutions and the like may be made therein without departing from its true scope.

I claim as my invention:

1. A settable, viscous, putty-like composition consisting essentially of, in combination, an intimate admixture of (a) a major proportion of a compound having a ratio of hydrogen atoms to all other atoms therein within the range of from 0.521 to 2:1 and being selected from at least one of the group consisting of polyethylene, butyl rubber, paraffin, polyisobutylene, and polyisoprene, (b) from 0.5% to 10% by Weight of boron, and (c) a fluid resinous carrier selected from at least one of the group consisting of fluid polyesters, epoxy resins, castable phenol-aldehyde resins, butadiene polymers and copoly- 5 mers thereof with styrene, butadieneacrylonitrile copolymers and plastisols, said composition when cured being adapted to attenuate fast moving neutrons and capture slow moving neutrons.

2. A settable, viscous, putty-like composition adapted to attenuate fast moving neutrons and capture slow moving neutrons consisting essentially of an intimate admixture of from 0.5% to 10% by weight of boron carbide and from 10% to by weight of polyethylene and a fluid resinous carrier selected from at least one of the group consisting of fluid polyesters, epoxy resins, castable phenol-aldehyde resins, butadiene polymers and copolymers thereof with styrene, butadieneacrylonitrile copolymers and plastisols.

3. A process for shielding a radioactive area to prevent the escape therefrom of neutron radiation which comprises applying to such area a settable viscous, puttylike composition consisting essentially of an intimate mixture of from 0.5% to 10% by weight of boron carbide and from 10% to 85% by weight of finely divided polyethylene, and a fluid resinous carrier selected from at least one of the group consisting of fluid polyesters, epoxy resins, castable phenol-aldehyde resins, butadiene polymers and copolymers thereof with styrene, butadieneacrylonitrile copolymers and plastisols, and curing said composition to a solid, said solid composition serving to attenuate fast moving neutrons and capture slow moving neutrons.

4. An article of manufacture comprising a member adapted to carry radioactive material and a body of molded, solid radiation shielding material applied thereto, said shielding material being adapted to attenuate fast moving neutrons and capture slow moving neutrons and consisting essentially of, in combination, an intimate mixture of (a) a compound having a ratio of hydrogen atoms to all other atoms therein within the range of from 0.5:1 to 2:1 and being selected from at least one of the group consisting of polyethylene, butyl rubber, paraffin, polyiso butylene, and polyisoprene, (b) and from 0.5% to 10% by weight of boron in (c) a carrier selected from at least one of the group consisting of fluid polyesters, epoxy resins, castable phenol-aldehyde resins, butadiene polymers and copolymers thereof with styrene, butadieneacrylonitrile copolymers and plastisols.

References Cited in the file of this patent UNITED STATES PATENTS 2,162,178 Marasco et al June 13, 1939 2,796,411 Zirkle June 18, 1957 FOREIGN PATENTS 513,838 Great Britain 1939 OTHER REFERENCES September 1954, 

1. A SETTABLE, VISCOUS, PUTTY-LIKE COMPOSITION CONSISTING ESSENTIALLY OF, IN COMBINATION, AN INTIMATE ADMIXTURE OF (A) A MAJOR PROPORTION OF A COMPOUND HAVING A RATIO OF HYDROGEN ATOMS TO ALL OTHER ATOMS THERIN WITHIN THE RANGE OF FROM 0.5:1 TO 2:1 AND BEING SELECTED FROM AT LEAST ONE OF THE GROUP CONSISTING OF POLYETHYLENE, BUTYL RUBBER, PARAFFIN, POLYISOBUTYLENE, AND POLYISOPRENE, (B) FORM 0.5% TO 10% BY WEIGHT OF BORON, AND (C) A FLUID RESINOUS CARRIER SELECTED FROM AT LEAST ONE OF THE GROUP CONSISTING OF FLUID POLYESTERS, EPOXY RESINS, CASTABLE PHENOL-ALDEHYDE RESIN, BUTADIENE POLYMERS AND COPOLYMERS THEREOF WITH STYRENE, BUTADIENEACRYLONITRILE COPOLYMERS AND PLASTISOLS, SAID COMPOSITION WHEN CURED BEING ADAPTED TO ATTENUATE FAST MOVING NEUTRONS AND CAPTURE SLOW MOVING NEUTRONS. 